Thermal compensator alloys used for timepiece balance springs are for the large part the product of the work of Charles-Edouard Guillaume and based on Fe—Ni—Cr Elinvar. Hardening elements have, since, been added: W+C, or Ti+Al, or Be, or Nb, which have in particular given birth to the alloys “Elinvar”, “Ni-Span”, “Nivarox”, “Isoval”.
All these alloys, which are suitable for application because of their mechanical properties, are however ferromagnetic, and therefore sensitive to magnetic fields, which is prejudicial to the functioning of a watch.
In the years 1970-1990, works on anti-ferromagnetic alloys were published but did not give rise to industrial developments. These alloys are almost insensitive to the effect of a magnetic field but have some industrial problems and the arrival of a clockmaking crisis in the 1980s stopped developments.
The document EP2924514 in the name of NIVAROX SA describes a timepiece spring or jewellery produced in a stainless steel alloy comprising a base formed from iron and chromium, arranged according to an austenitic face-centred cubic structure, and comprising manganese and nitrogen, and the composition of which spring by mass is:                chromium: minimum value 15%, maximum value 25%;        manganese: minimum value 5%, maximum value 25%;        nitrogen: minimum value 0.10%, maximum value 0.90%;        carbon: minimum value 0.10%, maximum value 1.00%;        with the total (C+N) of the values by mass of the carbon and nitrogen as a proportion of the total between 0.40% and 1.50%;        with the ratio (C/N) of the content by mass of the carbon as a proportion of the total relative to that of nitrogen between 0.125 and 0.550;        impurities and other metals with the exception of iron; minimum value 0%, maximum value 12.0%;        iron: the complement to 100%.        